core: add cgroup memory controller support on the unified hierarchy (#3315)

On the unified hierarchy, memory controller implements three control knobs -
low, high and max which enables more useable and versatile control over memory
usage.  This patch implements support for the three control knobs.

* MemoryLow, MemoryHigh and MemoryMax are added for memory.low, memory.high and
  memory.max, respectively.

* As all absolute limits on the unified hierarchy use "max" for no limit, make
  memory limit parse functions accept "max" in addition to "infinity" and
  document "max" for the new knobs.

* Implement compatibility translation between MemoryMax and MemoryLimit.

v2:

- Fixed missing else's in config_parse_memory_limit().
- Fixed missing newline when writing out drop-ins.
- Coding style updates to use "val > 0" instead of "val".
- Minor updates to documentation.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c
index f68c4a41ac..502e98d9dc 100644
--- a/src/shared/bus-unit-util.c
+++ b/src/shared/bus-unit-util.c
@@ -166,11 +166,11 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
 
                 r = sd_bus_message_append(m, "v", "b", r);
 
-        } else if (streq(field, "MemoryLimit")) {
+        } else if (STR_IN_SET(field, "MemoryLow", "MemoryHigh", "MemoryMax", "MemoryLimit")) {
                 uint64_t bytes;
 
-                if (isempty(eq) || streq(eq, "infinity"))
-                        bytes = (uint64_t) -1;
+                if (isempty(eq) || streq(eq, "max") || streq(eq, "infinity"))
+                        bytes = CGROUP_LIMIT_MAX;
                 else {
                         r = parse_size(eq, 1024, &bytes);
                         if (r < 0) {